1. Field of the Invention
The present invention relates to a vibration damping device to be used, for example, for an automobile engine mount.
2. Description of the Related Art
Conventionally, there has been known a vibration damping device as a type of vibration damping connector or vibration damping supporter interposed between a power unit and members constituting a vibration transmission system such as the vehicular body that connects the members to each other in a vibration-damping manner. This vibration damping device has a structure where an inner member is inserted into an outer cylindrical member, for example, and the inner member and the outer cylindrical member are elastically connected to each other by a main rubber elastic body.
Since the main rubber elastic body is provided to connect the inner member and the outer cylindrical member in the axis-perpendicular direction in a vibration damping device, the spring force in the axis-perpendicular direction is composed of compression and tension spring components of the main rubber elastic body, which allows the dynamic spring constant to be set high, while the spring force in the axial direction is composed of shear spring component of the main rubber elastic body, which made it difficult to set the dynamic spring constant high enough.
Now, U.S. Pat. No. 7,445,201 proposes a structure where the inner member is extended outward beyond the outer cylindrical member in the axial direction to place opposite to each other in the axial direction a first flange portion provided on the extension of the inner member and a second flange portion provided at the axial end portion of the outer cylindrical member, while the first and second flange portions are elastically connected by a connecting rubber in the axial direction. According to this structure, since the dynamic spring constant in the axial direction can be set high based on the compression and tension spring components of the connecting rubber, the spring constant becomes adjustable with a high degree of freedom not only in the axis-perpendicular direction but also in the axial direction.
However, in the structure of U.S. Pat. No. 7,445,201, as one tries to secure a large space for arranging the connecting rubber, there will be a need for extending the inner member beyond the outer cylindrical member in the axial direction to protrude substantially outward in the axial direction depending on the configuration of the inner member, as shown in FIG. 5 of U.S. Pat. No. 7,445,201, and this may cause a problem such as increase in size in the axial direction and increased weight. In addition, a first flange portion needs to be formed on the inner member to support the connecting rubber, which could pose problems including further increase in the weight and complication in shape of the inner member.